RFC 4979 XMPP Enumservice August 20071. Introduction
E.164 Number Mapping (ENUM) [1] uses the Domain Name System (DNS) [6]
to refer from E.164 numbers [7] to Uniform Resource Identifiers
(URIs) [3]. Specific services to be used with ENUM must be
registered with IANA. Section 3 of RFC 3761 describes the process of
such an Enumservice registration.
The Extensible Messaging and Presence Protocol (XMPP) [9] provides
means for streaming Extensible Markup Language (XML) [8] elements
between endpoints in close to real time. The XMPP framework is
mainly used to provide instant messaging, presence, and streaming
media services.
RFC 4622 [5] registers a Uniform Resource Identifier (URI) scheme for
identifying an XMPP entity as a URI or as an Internationalized
Resource Identifier (IRI) [4]. The Enumservice specified in this
document allows the provisioning of such "xmpp" URIs (and the URI
representations of "xmpp" IRIs) in ENUM.
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [2].
3. Enumservice Registration - XMPP
The following template contains information required for the IANA
registrations of the 'XMPP' Enumservice, according to Section 3 of
RFC 3761:
Enumservice Name: "XMPP"
Enumservice Type: "xmpp"
Enumservice Subtype: n/a
URI Schemes: "xmpp"
Functional Specification:
This Enumservice indicates that the resource identified is an XMPP
entity.
Security Considerations: see Section 6Mayrhofer Standards Track [Page 2]

RFC 4979 XMPP Enumservice August 2007
Intended Usage: COMMON
Author: Alexander Mayrhofer <alexander.mayrhofer@enum.at>
4. XMPP IRI/URI Considerations for ENUM4.1. Authority Component
XMPP IRIs/URIs optionally contain an "Authority Component" (see
Section 2.3 of RFC 4622). The presence of such an Authority
Component in an IRI/URI signals the processing application to
authenticate as the user indicated in the URI/IRI rather than using
the preconfigured identity.
In the context of this Enumservice, arbitrary clients may discover
and use the XMPP URIs/IRIs associated to an E.164 number. Hence, in
most cases, those clients will not be able to authenticate as
requested in the Authority Component.
Therefore, URIs/IRIs that result from processing an XMPP Enumservice
record SHOULD NOT contain an Authority Component.
4.2. IRI-to-URI mapping
While XMPP supports IRIs as well as 'plain' URIs, ENUM itself
supports only the use of URIs for Enumservices.
Therefore, XMPP IRIs MUST be mapped to URIs for use in an XMPP
Enumservice record. The mapping MUST follow the procedures outlined
in Section 3.1 of RFC 3987.
5. Example
An example ENUM entry referencing to a XMPP URI could look like:
$ORIGIN 6.9.4.0.6.9.4.5.1.1.4.4.e164.arpa.
@ IN NAPTR ( 100 10 "u"
"E2U+xmpp"
"!^.*$!xmpp:some-user@example.com!" .
)
Mayrhofer Standards Track [Page 3]

RFC 4979 XMPP Enumservice August 20076. Security and Privacy Considerations
General security considerations of the protocols on which this
Enumservice registration is based are addressed in Sections 3.1.3 and
6 of RFC 3761 (ENUM) and Section 14 of RFC 3920 (XMPP).
Since ENUM uses DNS -- a publicly available database -- any
information contained in records provisioned in ENUM domains must be
considered public as well. Even after revoking the DNS entry and
removing the referred resource, copies of the information could still
be available.
Information published in ENUM records could reveal associations
between E.164 numbers and their owners -- especially if IRIs/URIs
contain personal identifiers or domain names for which ownership
information can be obtained easily.
However, it is important to note that the ENUM record itself does not
need to contain any personal information. It just points to a
location where access to personal information could be granted.
ENUM records pointing to third-party resources can easily be
provisioned on purpose by the ENUM domain owner -- so any assumption
about the association between a number and an entity could therefore
be completely bogus unless some kind of identity verification is in
place. This verification is out of scope for this memo.
7. IANA Considerations
This memo requests IANA to add a new "XMPP" Enumservice to the
'Enumservice Registrations' registry, according to the definitions in
this document and RFC 3761 [1].
The required template is contained in Section 3.
8. Acknowledgements
Some text from RFC 4622 was used in the Introduction of this
document. Charles Clancy, Miguel Garcia, Andrew Newton, Jon
Peterson, and Peter Saint-Andre provided extensive reviews and
valuable feedback.
Mayrhofer Standards Track [Page 4]

RFC 4979 XMPP Enumservice August 2007
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Mayrhofer Standards Track [Page 7]